diff --git a/README.md b/README.md
index e731e5f..0ad06a8 100644
--- a/README.md
+++ b/README.md
@@ -336,7 +336,9 @@
 
 ## Running the tests
 
-The tests are all built from the tests/ directory.
+The tests are all built from the tests/ directory. There is a separate
+directory `benchmarks/` containing benchmarks, and that has its own
+documentation on [running the benchmarks](benchmarks/README.md).
 
 ### Device tests
 
diff --git a/libc/Android.bp b/libc/Android.bp
index 8a88a0e..7098ab1 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -791,6 +791,7 @@
         "bionic/abort.cpp",
         "bionic/accept.cpp",
         "bionic/access.cpp",
+        "bionic/android_crash_detail.cpp",
         "bionic/android_set_abort_message.cpp",
         "bionic/android_unsafe_frame_pointer_chase.cpp",
         "bionic/arpa_inet.cpp",
diff --git a/libc/bionic/__bionic_get_shell_path.cpp b/libc/bionic/__bionic_get_shell_path.cpp
index b78aede..5d22e00 100644
--- a/libc/bionic/__bionic_get_shell_path.cpp
+++ b/libc/bionic/__bionic_get_shell_path.cpp
@@ -28,29 +28,11 @@
 
 #include "private/__bionic_get_shell_path.h"
 
-#include <errno.h>
-#include <string.h>
-#include <sys/cdefs.h>
-#include <unistd.h>
-
-#define VENDOR_PREFIX "/vendor/"
-
-static const char* init_sh_path() {
+const char* __bionic_get_shell_path() {
 #if !defined(__ANDROID__)
   // For the host Bionic, use the standard /bin/sh
   return "/bin/sh";
 #else
-  // Look for /system or /vendor prefix.
-  char exe_path[strlen(VENDOR_PREFIX)];
-  ssize_t len = readlink("/proc/self/exe", exe_path, sizeof(exe_path));
-  if (len != -1 && !strncmp(exe_path, VENDOR_PREFIX, strlen(VENDOR_PREFIX))) {
-    return "/vendor/bin/sh";
-  }
   return "/system/bin/sh";
 #endif  // if !defined(__ANDROID__)
 }
-
-const char* __bionic_get_shell_path() {
-  static const char* sh_path = init_sh_path();
-  return sh_path;
-}
diff --git a/libc/bionic/android_crash_detail.cpp b/libc/bionic/android_crash_detail.cpp
new file mode 100644
index 0000000..30ce505
--- /dev/null
+++ b/libc/bionic/android_crash_detail.cpp
@@ -0,0 +1,122 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <android/crash_detail.h>
+
+#include <async_safe/log.h>
+#include <bionic/crash_detail_internal.h>
+
+#include <bits/stdatomic.h>
+#include <pthread.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/prctl.h>
+
+#include "private/ScopedPthreadMutexLocker.h"
+#include "private/bionic_defs.h"
+#include "private/bionic_globals.h"
+
+static _Atomic(crash_detail_t*) free_head = nullptr;
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+crash_detail_t* android_crash_detail_register(const void* name, size_t name_size, const void* data,
+                                              size_t data_size) {
+  auto populate_crash_detail = [&](crash_detail_t* result) {
+    result->name = reinterpret_cast<const char*>(name);
+    result->name_size = name_size;
+    result->data = reinterpret_cast<const char*>(data);
+    result->data_size = data_size;
+  };
+  // This is a atomic fast-path for RAII use-cases where the app keeps creating and deleting
+  // crash details for short periods of time to capture detailed scopes.
+  if (crash_detail_t* head = atomic_load(&free_head)) {
+    while (head != nullptr && !atomic_compare_exchange_strong(&free_head, &head, head->prev_free)) {
+      // intentionally left blank.
+    }
+    if (head) {
+      head->prev_free = nullptr;
+      populate_crash_detail(head);
+      return head;
+    }
+  }
+  ScopedPthreadMutexLocker locker(&__libc_shared_globals()->crash_detail_page_lock);
+  struct crash_detail_page_t* prev = nullptr;
+  struct crash_detail_page_t* page = __libc_shared_globals()->crash_detail_page;
+  if (page != nullptr && page->used == kNumCrashDetails) {
+    prev = page;
+    page = nullptr;
+  }
+  if (page == nullptr) {
+    size_t size = sizeof(crash_detail_page_t);
+    void* map = mmap(nullptr, size, PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);
+    if (map == MAP_FAILED) {
+      async_safe_format_log(ANDROID_LOG_ERROR, "libc", "failed to allocate crash_detail_page: %m");
+      return nullptr;
+    }
+    prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, map, size, "crash details");
+    page = reinterpret_cast<struct crash_detail_page_t*>(map);
+    page->prev = prev;
+    __libc_shared_globals()->crash_detail_page = page;
+  }
+  crash_detail_t* result = &page->crash_details[page->used];
+  populate_crash_detail(result);
+  page->used++;
+  return result;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+void android_crash_detail_unregister(crash_detail_t* crash_detail) {
+  if (crash_detail) {
+    if (crash_detail->prev_free) {
+      // removing already removed would mess up the free-list by creating a circle.
+      return;
+    }
+    crash_detail->data = nullptr;
+    crash_detail->name = nullptr;
+    crash_detail_t* prev = atomic_load(&free_head);
+    do {
+      crash_detail->prev_free = prev;
+    } while (!atomic_compare_exchange_strong(&free_head, &prev, crash_detail));
+  }
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+void android_crash_detail_replace_data(crash_detail_t* crash_detail, const void* data,
+                                       size_t data_size) {
+  crash_detail->data = reinterpret_cast<const char*>(data);
+  crash_detail->data_size = data_size;
+}
+
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+void android_crash_detail_replace_name(crash_detail_t* crash_detail, const void* name,
+                                       size_t name_size) {
+  crash_detail->name = reinterpret_cast<const char*>(name);
+  crash_detail->name_size = name_size;
+}
diff --git a/libc/bionic/android_set_abort_message.cpp b/libc/bionic/android_set_abort_message.cpp
index 53d7576..05adf3e 100644
--- a/libc/bionic/android_set_abort_message.cpp
+++ b/libc/bionic/android_set_abort_message.cpp
@@ -29,7 +29,6 @@
 #include <android/set_abort_message.h>
 
 #include <async_safe/log.h>
-#include <bionic/set_abort_message_internal.h>
 
 #include <bits/stdatomic.h>
 #include <pthread.h>
@@ -60,8 +59,6 @@
               "The in-memory layout of magic_abort_msg_t is not consistent with what automated "
               "tools expect.");
 
-static _Atomic(crash_detail_t*) free_head = nullptr;
-
 [[clang::optnone]]
 static void fill_abort_message_magic(magic_abort_msg_t* new_magic_abort_message) {
   // 128-bit magic for the abort message. Chosen by fair dice roll.
@@ -103,65 +100,3 @@
   strcpy(new_magic_abort_message->msg.msg, msg);
   __libc_shared_globals()->abort_msg = &new_magic_abort_message->msg;
 }
-
-__BIONIC_WEAK_FOR_NATIVE_BRIDGE
-crash_detail_t* android_register_crash_detail(const void* name, size_t name_size, const void* data,
-                                              size_t data_size) {
-  auto populate_crash_detail = [&](crash_detail_t* result) {
-    result->name = reinterpret_cast<const char*>(name);
-    result->name_size = name_size;
-    result->data = reinterpret_cast<const char*>(data);
-    result->data_size = data_size;
-  };
-  // This is a atomic fast-path for RAII use-cases where the app keeps creating and deleting
-  // crash details for short periods of time to capture detailed scopes.
-  if (crash_detail_t* head = atomic_load(&free_head)) {
-    while (head != nullptr && !atomic_compare_exchange_strong(&free_head, &head, head->prev_free)) {
-      // intentionally left blank.
-    }
-    if (head) {
-      head->prev_free = nullptr;
-      populate_crash_detail(head);
-      return head;
-    }
-  }
-  ScopedPthreadMutexLocker locker(&__libc_shared_globals()->crash_detail_page_lock);
-  struct crash_detail_page_t* prev = nullptr;
-  struct crash_detail_page_t* page = __libc_shared_globals()->crash_detail_page;
-  if (page != nullptr && page->used == kNumCrashDetails) {
-    prev = page;
-    page = nullptr;
-  }
-  if (page == nullptr) {
-    size_t size = sizeof(crash_detail_page_t);
-    void* map = mmap(nullptr, size, PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);
-    if (map == MAP_FAILED) {
-      async_safe_format_log(ANDROID_LOG_ERROR, "libc", "failed to allocate crash_detail_page: %m");
-      return nullptr;
-    }
-    prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, map, size, "crash details");
-    page = reinterpret_cast<struct crash_detail_page_t*>(map);
-    page->prev = prev;
-    __libc_shared_globals()->crash_detail_page = page;
-  }
-  crash_detail_t* result = &page->crash_details[page->used];
-  populate_crash_detail(result);
-  page->used++;
-  return result;
-}
-
-__BIONIC_WEAK_FOR_NATIVE_BRIDGE
-void android_unregister_crash_detail(crash_detail_t* crash_detail) {
-  if (crash_detail) {
-    if (crash_detail->prev_free) {
-      // removing already removed would mess up the free-list by creating a circle.
-      return;
-    }
-    crash_detail->data = nullptr;
-    crash_detail->name = nullptr;
-    crash_detail_t* prev = atomic_load(&free_head);
-    do {
-      crash_detail->prev_free = prev;
-    } while (!atomic_compare_exchange_strong(&free_head, &prev, crash_detail));
-  }
-}
diff --git a/libc/bionic/heap_tagging.cpp b/libc/bionic/heap_tagging.cpp
index 48ec955..0c1e506 100644
--- a/libc/bionic/heap_tagging.cpp
+++ b/libc/bionic/heap_tagging.cpp
@@ -57,6 +57,7 @@
         break;
       case M_HEAP_TAGGING_LEVEL_SYNC:
       case M_HEAP_TAGGING_LEVEL_ASYNC:
+        atomic_store(&globals->memtag, true);
         atomic_store(&globals->memtag_stack, __libc_shared_globals()->initial_memtag_stack);
         break;
       default:
@@ -113,6 +114,7 @@
           globals->heap_pointer_tag = static_cast<uintptr_t>(0xffull << UNTAG_SHIFT);
         }
         atomic_store(&globals->memtag_stack, false);
+        atomic_store(&globals->memtag, false);
       });
 
       if (heap_tagging_level != M_HEAP_TAGGING_LEVEL_TBI) {
diff --git a/libc/bionic/libc_init_dynamic.cpp b/libc/bionic/libc_init_dynamic.cpp
index c61810e..1180a51 100644
--- a/libc/bionic/libc_init_dynamic.cpp
+++ b/libc/bionic/libc_init_dynamic.cpp
@@ -39,11 +39,12 @@
  *   all dynamic linking has been performed.
  */
 
+#include <elf.h>
 #include <stddef.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <stdint.h>
-#include <elf.h>
+#include "bionic/pthread_internal.h"
 #include "libc_init_common.h"
 
 #include "private/bionic_defs.h"
@@ -59,6 +60,11 @@
   extern int __cxa_atexit(void (*)(void *), void *, void *);
 };
 
+void memtag_stack_dlopen_callback() {
+  async_safe_format_log(ANDROID_LOG_INFO, "libc", "remapping stacks as PROT_MTE");
+  __pthread_internal_remap_stack_with_mte();
+}
+
 // Use an initializer so __libc_sysinfo will have a fallback implementation
 // while .preinit_array constructors run.
 #if defined(__i386__)
@@ -156,6 +162,10 @@
 
   __libc_init_mte_late();
 
+  // This roundabout way is needed so we don't use the static libc linked into the linker, which
+  // will not affect the process.
+  __libc_shared_globals()->memtag_stack_dlopen_callback = memtag_stack_dlopen_callback;
+
   exit(slingshot(args.argc - __libc_shared_globals()->initial_linker_arg_count,
                  args.argv + __libc_shared_globals()->initial_linker_arg_count,
                  args.envp));
diff --git a/libc/bionic/libc_init_static.cpp b/libc/bionic/libc_init_static.cpp
index 00faa5b..f091ff8 100644
--- a/libc/bionic/libc_init_static.cpp
+++ b/libc/bionic/libc_init_static.cpp
@@ -305,6 +305,14 @@
   bool memtag_stack = false;
   HeapTaggingLevel level =
       __get_tagging_level(memtag_dynamic_entries, phdr_start, phdr_ct, load_bias, &memtag_stack);
+  // This is used by the linker (in linker.cpp) to communicate than any library linked by this
+  // executable enables memtag-stack.
+  if (__libc_shared_globals()->initial_memtag_stack) {
+    if (!memtag_stack) {
+      async_safe_format_log(ANDROID_LOG_INFO, "libc", "enabling PROT_MTE as requested by linker");
+    }
+    memtag_stack = true;
+  }
   char* env = getenv("BIONIC_MEMTAG_UPGRADE_SECS");
   static const char kAppProcessName[] = "app_process64";
   const char* progname = __libc_shared_globals()->init_progname;
@@ -373,6 +381,8 @@
   }
   // We did not enable MTE, so we do not need to arm the upgrade timer.
   __libc_shared_globals()->heap_tagging_upgrade_timer_sec = 0;
+  // We also didn't enable memtag_stack.
+  __libc_shared_globals()->initial_memtag_stack = false;
 }
 #else   // __aarch64__
 void __libc_init_mte(const memtag_dynamic_entries_t*, const void*, size_t, uintptr_t, void*) {}
diff --git a/libc/bionic/pathconf.cpp b/libc/bionic/pathconf.cpp
index 9724f44..9bbecc3 100644
--- a/libc/bionic/pathconf.cpp
+++ b/libc/bionic/pathconf.cpp
@@ -107,14 +107,6 @@
     case _PC_REC_MIN_XFER_SIZE:
       return s.f_bsize;
 
-#if 0
-    case _PC_REC_INCR_XFER_SIZE:
-    case _PC_REC_MAX_XFER_SIZE:
-#endif
-
-    case _PC_SYMLINK_MAX:
-      return -1; /* no limit */
-
     case _PC_CHOWN_RESTRICTED:
       return _POSIX_CHOWN_RESTRICTED;
 
@@ -125,12 +117,15 @@
       return _POSIX_VDISABLE;
 
     case _PC_ASYNC_IO:
-      return -1;
-
     case _PC_PRIO_IO:
-      return -1;
-
+    case _PC_REC_INCR_XFER_SIZE:
+    case _PC_REC_MAX_XFER_SIZE:
+    case _PC_SYMLINK_MAX:
     case _PC_SYNC_IO:
+      // No API to answer these: the caller will have to "try it and see".
+      // This differs from the next case in not setting errno to EINVAL,
+      // since we did understand the question --- we just don't have a
+      // good answer.
       return -1;
 
     default:
diff --git a/libc/bionic/pthread_attr.cpp b/libc/bionic/pthread_attr.cpp
index de4cc9e..f6c0401 100644
--- a/libc/bionic/pthread_attr.cpp
+++ b/libc/bionic/pthread_attr.cpp
@@ -155,36 +155,6 @@
   return 0;
 }
 
-static uintptr_t __get_main_stack_startstack() {
-  FILE* fp = fopen("/proc/self/stat", "re");
-  if (fp == nullptr) {
-    async_safe_fatal("couldn't open /proc/self/stat: %m");
-  }
-
-  char line[BUFSIZ];
-  if (fgets(line, sizeof(line), fp) == nullptr) {
-    async_safe_fatal("couldn't read /proc/self/stat: %m");
-  }
-
-  fclose(fp);
-
-  // See man 5 proc. There's no reason comm can't contain ' ' or ')',
-  // so we search backwards for the end of it. We're looking for this field:
-  //
-  //  startstack %lu (28) The address of the start (i.e., bottom) of the stack.
-  uintptr_t startstack = 0;
-  const char* end_of_comm = strrchr(line, ')');
-  if (sscanf(end_of_comm + 1, " %*c "
-             "%*d %*d %*d %*d %*d "
-             "%*u %*u %*u %*u %*u %*u %*u "
-             "%*d %*d %*d %*d %*d %*d "
-             "%*u %*u %*d %*u %*u %*u %" SCNuPTR, &startstack) != 1) {
-    async_safe_fatal("couldn't parse /proc/self/stat");
-  }
-
-  return startstack;
-}
-
 static int __pthread_attr_getstack_main_thread(void** stack_base, size_t* stack_size) {
   ErrnoRestorer errno_restorer;
 
@@ -198,28 +168,11 @@
   if (stack_limit.rlim_cur == RLIM_INFINITY) {
     stack_limit.rlim_cur = 8 * 1024 * 1024;
   }
-
-  // Ask the kernel where our main thread's stack started.
-  uintptr_t startstack = __get_main_stack_startstack();
-
-  // Hunt for the region that contains that address.
-  FILE* fp = fopen("/proc/self/maps", "re");
-  if (fp == nullptr) {
-    async_safe_fatal("couldn't open /proc/self/maps: %m");
-  }
-  char line[BUFSIZ];
-  while (fgets(line, sizeof(line), fp) != nullptr) {
-    uintptr_t lo, hi;
-    if (sscanf(line, "%" SCNxPTR "-%" SCNxPTR, &lo, &hi) == 2) {
-      if (lo <= startstack && startstack <= hi) {
-        *stack_size = stack_limit.rlim_cur;
-        *stack_base = reinterpret_cast<void*>(hi - *stack_size);
-        fclose(fp);
-        return 0;
-      }
-    }
-  }
-  async_safe_fatal("stack not found in /proc/self/maps");
+  uintptr_t lo, hi;
+  __find_main_stack_limits(&lo, &hi);
+  *stack_size = stack_limit.rlim_cur;
+  *stack_base = reinterpret_cast<void*>(hi - *stack_size);
+  return 0;
 }
 
 __BIONIC_WEAK_FOR_NATIVE_BRIDGE
diff --git a/libc/bionic/pthread_internal.cpp b/libc/bionic/pthread_internal.cpp
index 6a7ee2f..bfe2f98 100644
--- a/libc/bionic/pthread_internal.cpp
+++ b/libc/bionic/pthread_internal.cpp
@@ -40,6 +40,7 @@
 #include "private/ErrnoRestorer.h"
 #include "private/ScopedRWLock.h"
 #include "private/bionic_futex.h"
+#include "private/bionic_globals.h"
 #include "private/bionic_tls.h"
 
 static pthread_internal_t* g_thread_list = nullptr;
@@ -119,6 +120,89 @@
   return nullptr;
 }
 
+static uintptr_t __get_main_stack_startstack() {
+  FILE* fp = fopen("/proc/self/stat", "re");
+  if (fp == nullptr) {
+    async_safe_fatal("couldn't open /proc/self/stat: %m");
+  }
+
+  char line[BUFSIZ];
+  if (fgets(line, sizeof(line), fp) == nullptr) {
+    async_safe_fatal("couldn't read /proc/self/stat: %m");
+  }
+
+  fclose(fp);
+
+  // See man 5 proc. There's no reason comm can't contain ' ' or ')',
+  // so we search backwards for the end of it. We're looking for this field:
+  //
+  //  startstack %lu (28) The address of the start (i.e., bottom) of the stack.
+  uintptr_t startstack = 0;
+  const char* end_of_comm = strrchr(line, ')');
+  if (sscanf(end_of_comm + 1,
+             " %*c "
+             "%*d %*d %*d %*d %*d "
+             "%*u %*u %*u %*u %*u %*u %*u "
+             "%*d %*d %*d %*d %*d %*d "
+             "%*u %*u %*d %*u %*u %*u %" SCNuPTR,
+             &startstack) != 1) {
+    async_safe_fatal("couldn't parse /proc/self/stat");
+  }
+
+  return startstack;
+}
+
+void __find_main_stack_limits(uintptr_t* low, uintptr_t* high) {
+  // Ask the kernel where our main thread's stack started.
+  uintptr_t startstack = __get_main_stack_startstack();
+
+  // Hunt for the region that contains that address.
+  FILE* fp = fopen("/proc/self/maps", "re");
+  if (fp == nullptr) {
+    async_safe_fatal("couldn't open /proc/self/maps: %m");
+  }
+  char line[BUFSIZ];
+  while (fgets(line, sizeof(line), fp) != nullptr) {
+    uintptr_t lo, hi;
+    if (sscanf(line, "%" SCNxPTR "-%" SCNxPTR, &lo, &hi) == 2) {
+      if (lo <= startstack && startstack <= hi) {
+        *low = lo;
+        *high = hi;
+        fclose(fp);
+        return;
+      }
+    }
+  }
+  async_safe_fatal("stack not found in /proc/self/maps");
+}
+
+void __pthread_internal_remap_stack_with_mte() {
+#if defined(__aarch64__)
+  // If process doesn't have MTE enabled, we don't need to do anything.
+  if (!__libc_globals->memtag) return;
+  bool prev = true;
+  __libc_globals.mutate(
+      [&prev](libc_globals* globals) { prev = atomic_exchange(&globals->memtag_stack, true); });
+  if (prev) return;
+  uintptr_t lo, hi;
+  __find_main_stack_limits(&lo, &hi);
+
+  if (mprotect(reinterpret_cast<void*>(lo), hi - lo,
+               PROT_READ | PROT_WRITE | PROT_MTE | PROT_GROWSDOWN)) {
+    async_safe_fatal("error: failed to set PROT_MTE on main thread");
+  }
+  ScopedWriteLock creation_locker(&g_thread_creation_lock);
+  ScopedReadLock list_locker(&g_thread_list_lock);
+  for (pthread_internal_t* t = g_thread_list; t != nullptr; t = t->next) {
+    if (t->terminating || t->is_main()) continue;
+    if (mprotect(t->mmap_base_unguarded, t->mmap_size_unguarded,
+                 PROT_READ | PROT_WRITE | PROT_MTE)) {
+      async_safe_fatal("error: failed to set PROT_MTE on thread: %d", t->tid);
+    }
+  }
+#endif
+}
+
 bool android_run_on_all_threads(bool (*func)(void*), void* arg) {
   // Take the locks in this order to avoid inversion (pthread_create ->
   // __pthread_internal_add).
diff --git a/libc/bionic/pthread_internal.h b/libc/bionic/pthread_internal.h
index 3b9e6a4..091f711 100644
--- a/libc/bionic/pthread_internal.h
+++ b/libc/bionic/pthread_internal.h
@@ -178,6 +178,7 @@
   bionic_tls* bionic_tls;
 
   int errno_value;
+  bool is_main() { return start_routine == nullptr; }
 };
 
 struct ThreadMapping {
@@ -207,6 +208,7 @@
 __LIBC_HIDDEN__ pid_t __pthread_internal_gettid(pthread_t pthread_id, const char* caller);
 __LIBC_HIDDEN__ void __pthread_internal_remove(pthread_internal_t* thread);
 __LIBC_HIDDEN__ void __pthread_internal_remove_and_free(pthread_internal_t* thread);
+__LIBC_HIDDEN__ void __find_main_stack_limits(uintptr_t* low, uintptr_t* high);
 
 static inline __always_inline bionic_tcb* __get_bionic_tcb() {
   return reinterpret_cast<bionic_tcb*>(&__get_tls()[MIN_TLS_SLOT]);
@@ -266,6 +268,9 @@
 __LIBC_HIDDEN__ extern void __bionic_atfork_run_child();
 __LIBC_HIDDEN__ extern void __bionic_atfork_run_parent();
 
+// Re-map all threads and successively launched threads with PROT_MTE.
+__LIBC_HIDDEN__ void __pthread_internal_remap_stack_with_mte();
+
 extern "C" bool android_run_on_all_threads(bool (*func)(void*), void* arg);
 
 extern pthread_rwlock_t g_thread_creation_lock;
diff --git a/libc/bionic/sysconf.cpp b/libc/bionic/sysconf.cpp
index ff72b93..9ffb58e 100644
--- a/libc/bionic/sysconf.cpp
+++ b/libc/bionic/sysconf.cpp
@@ -41,16 +41,6 @@
 #include "platform/bionic/page.h"
 #include "private/bionic_tls.h"
 
-static long __sysconf_fread_long(const char* path) {
-  long result = 0;
-  FILE* fp = fopen(path, "re");
-  if (fp != nullptr) {
-    fscanf(fp, "%ld", &result);
-    fclose(fp);
-  }
-  return result;
-}
-
 struct sysconf_cache {
   long size, assoc, linesize;
 
@@ -100,6 +90,16 @@
 
 #else
 
+static long __sysconf_fread_long(const char* path) {
+  long result = 0;
+  FILE* fp = fopen(path, "re");
+  if (fp != nullptr) {
+    fscanf(fp, "%ld", &result);
+    fclose(fp);
+  }
+  return result;
+}
+
 static sysconf_caches* __sysconf_caches() {
   static sysconf_caches cached = []{
     sysconf_caches info = {};
@@ -182,8 +182,8 @@
 
     case _SC_AVPHYS_PAGES:      return get_avphys_pages();
     case _SC_CHILD_MAX:         return __sysconf_rlimit(RLIMIT_NPROC);
-    case _SC_CLK_TCK:           return static_cast<long>(getauxval(AT_CLKTCK));
-    case _SC_NGROUPS_MAX:       return __sysconf_fread_long("/proc/sys/kernel/ngroups_max");
+    case _SC_CLK_TCK:
+      return static_cast<long>(getauxval(AT_CLKTCK));
     case _SC_NPROCESSORS_CONF:  return get_nprocs_conf();
     case _SC_NPROCESSORS_ONLN:  return get_nprocs();
     case _SC_OPEN_MAX:          return __sysconf_rlimit(RLIMIT_NOFILE);
@@ -205,6 +205,11 @@
     case _SC_COLL_WEIGHTS_MAX:  return _POSIX2_COLL_WEIGHTS_MAX;  // Minimum requirement.
     case _SC_EXPR_NEST_MAX:     return _POSIX2_EXPR_NEST_MAX;     // Minimum requirement.
     case _SC_LINE_MAX:          return _POSIX2_LINE_MAX;          // Minimum requirement.
+    case _SC_NGROUPS_MAX:
+      // Only root can read /proc/sys/kernel/ngroups_max on Android, and groups
+      // are vestigial anyway, so the "maximum maximum" of NGROUPS_MAX is a good
+      // enough answer for _SC_NGROUPS_MAX...
+      return NGROUPS_MAX;
     case _SC_PASS_MAX:          return PASS_MAX;
     case _SC_2_C_BIND:          return _POSIX2_C_BIND;
     case _SC_2_C_DEV:           return _POSIX2_C_DEV;
diff --git a/libc/include/android/crash_detail.h b/libc/include/android/crash_detail.h
new file mode 100644
index 0000000..1fd082f
--- /dev/null
+++ b/libc/include/android/crash_detail.h
@@ -0,0 +1,123 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#pragma once
+
+/**
+ * @file android/crash_detail.h
+ * @brief Attach extra information to android crashes.
+ */
+
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+typedef struct crash_detail_t crash_detail_t;
+
+/**
+ * Register a new buffer to get logged into tombstones for crashes.
+ *
+ * It will be added to both the tombstone proto in the crash_detail field, and
+ * in the tombstone text format.
+ *
+ * Tombstone proto definition:
+ *   https://cs.android.com/android/platform/superproject/main/+/main:system/core/debuggerd/proto/tombstone.proto
+ *
+ * The lifetime of name and data has to be valid until the program crashes, or until
+ * android_crash_detail_unregister is called.
+ *
+ * Example usage:
+ *   const char* stageName = "garbage_collection";
+ *   crash_detail_t* cd = android_crash_detail_register("stage", stageName, strlen(stageName));
+ *   do_garbage_collection();
+ *   android_crash_detail_unregister(cd);
+ *
+ * If this example crashes in do_garbage_collection, a line will show up in the textual representation of the tombstone:
+ *   Extra crash detail: stage: 'garbage_collection'
+ *
+ * Introduced in API 35.
+ *
+ * \param name identifying name for this extra data.
+ *             this should generally be a human-readable debug string, but we are treating
+ *             it as arbitrary bytes because it could be corrupted by the crash.
+ * \param name_size number of bytes of the buffer pointed to by name
+ * \param data a buffer containing the extra detail bytes, if null the crash detail
+ *             is disabled until android_crash_detail_replace_data replaces it with
+ *             a non-null pointer.
+ * \param data_size number of bytes of the buffer pointed to by data
+ *
+ * \return a handle to the extra crash detail.
+ */
+crash_detail_t* _Nullable android_crash_detail_register(
+    const void* _Nonnull name, size_t name_size, const void* _Nullable data, size_t data_size) __INTRODUCED_IN(35);
+
+/**
+ * Unregister crash detail from being logged into tombstones.
+ *
+ * After this function returns, the lifetime of the objects crash_detail was
+ * constructed from no longer needs to be valid.
+ *
+ * Introduced in API 35.
+ *
+ * \param crash_detail the crash_detail that should be removed.
+ */
+void android_crash_detail_unregister(crash_detail_t* _Nonnull crash_detail) __INTRODUCED_IN(35);
+
+/**
+ * Replace data of crash detail.
+ *
+ * This is more efficient than using android_crash_detail_unregister followed by
+ * android_crash_detail_register. If you very frequently need to swap out the data,
+ * you can hold onto the crash_detail.
+ *
+ * Introduced in API 35.
+ *
+ * \param data the new buffer containing the extra detail bytes, or null to disable until
+ *             android_crash_detail_replace_data is called again with non-null data.
+ * \param data_size the number of bytes of the buffer pointed to by data.
+ */
+void android_crash_detail_replace_data(crash_detail_t* _Nonnull crash_detail, const void* _Nullable data, size_t data_size) __INTRODUCED_IN(35);
+
+/**
+ * Replace name of crash detail.
+ *
+ * This is more efficient than using android_crash_detail_unregister followed by
+ * android_crash_detail_register. If you very frequently need to swap out the name,
+ * you can hold onto the crash_detail.
+ *
+ * Introduced in API 35.
+ *
+ * \param name identifying name for this extra data.
+ * \param name_size number of bytes of the buffer pointed to by name
+ */
+void android_crash_detail_replace_name(crash_detail_t* _Nonnull crash_detail, const void* _Nonnull name, size_t name_size) __INTRODUCED_IN(35);
+
+__END_DECLS
diff --git a/libc/include/android/set_abort_message.h b/libc/include/android/set_abort_message.h
index e92c6ec..2525242 100644
--- a/libc/include/android/set_abort_message.h
+++ b/libc/include/android/set_abort_message.h
@@ -30,7 +30,7 @@
 
 /**
  * @file android/set_abort_message.h
- * @brief Attach extra information to android crashes.
+ * @brief The android_set_abort_message() function.
  */
 
 #include <stddef.h>
@@ -51,51 +51,4 @@
  */
 void android_set_abort_message(const char* _Nullable __msg);
 
-/**
- * Register a new buffer to get logged into tombstones for crashes.
- *
- * It will be added to both the tombstone proto in the crash_detail field, and
- * in the tombstone text format.
- *
- * Tombstone proto definition:
- *   https://cs.android.com/android/platform/superproject/main/+/main:system/core/debuggerd/proto/tombstone.proto
- *
- * The lifetime of name and data has to be valid until the program crashes, or until
- * android_unregister_crash_detail is called.
- *
- * Example usage:
- *   const char* stageName = "garbage_collection";
- *   crash_detail_t* cd = android_register_crash_detail("stage", stageName, strlen(stageName));
- *   do_garbage_collection();
- *   android_unregister_crash_detail(cd);
- *
- * If this example crashes in do_garbage_collection, a line will show up in the textual representation of the tombstone:
- *   Extra crash detail: stage: 'garbage_collection'
- *
- * Introduced in API 35.
- *
- * \param name identifying name for this extra data.
- *             this should generally be a human-readable debug string, but we are treating
- *             it as arbitrary bytes because it could be corrupted by the crash.
- * \param name_size number of bytes of the buffer pointed to by name
- * \param data a buffer containing the extra detail bytes
- * \param data_size number of bytes of the buffer pointed to by data
- *
- * \return a handle to the extra crash detail for use with android_unregister_crash_detail.
- */
-crash_detail_t* _Nullable android_register_crash_detail(
-    const void* _Nonnull name, size_t name_size, const void* _Nonnull data, size_t data_size) __INTRODUCED_IN(35);
-
-/**
- * Unregister crash detail from being logged into tombstones.
- *
- * After this function returns, the lifetime of the objects crash_detail was
- * constructed from no longer needs to be valid.
- *
- * Introduced in API 35.
- *
- * \param crash_detail the crash_detail that should be removed.
- */
-void android_unregister_crash_detail(crash_detail_t* _Nonnull crash_detail) __INTRODUCED_IN(35);
-
 __END_DECLS
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index ecdb25c..5e9763b 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -1586,8 +1586,10 @@
 
 LIBC_V { # introduced=VanillaIceCream
   global:
-    android_register_crash_detail;
-    android_unregister_crash_detail;
+    android_crash_detail_register;
+    android_crash_detail_unregister;
+    android_crash_detail_replace_name;
+    android_crash_detail_replace_data;
     epoll_pwait2;
     epoll_pwait2_64;
     localtime_rz;
diff --git a/libc/platform/bionic/set_abort_message_internal.h b/libc/platform/bionic/crash_detail_internal.h
similarity index 97%
rename from libc/platform/bionic/set_abort_message_internal.h
rename to libc/platform/bionic/crash_detail_internal.h
index 4dff3ac..d8508a5 100644
--- a/libc/platform/bionic/set_abort_message_internal.h
+++ b/libc/platform/bionic/crash_detail_internal.h
@@ -28,7 +28,7 @@
 
 #pragma once
 
-#include <android/set_abort_message.h>
+#include <android/crash_detail.h>
 #include <stddef.h>
 #include <sys/cdefs.h>
 
diff --git a/libc/private/bionic_globals.h b/libc/private/bionic_globals.h
index 23f2953..6f1e389 100644
--- a/libc/private/bionic_globals.h
+++ b/libc/private/bionic_globals.h
@@ -50,6 +50,7 @@
   uintptr_t heap_pointer_tag;
   _Atomic(bool) memtag_stack;
   _Atomic(bool) decay_time_enabled;
+  _Atomic(bool) memtag;
 
   // In order to allow a complete switch between dispatch tables without
   // the need for copying each function by function in the structure,
@@ -137,6 +138,7 @@
   bool initial_memtag_stack = false;
   int64_t heap_tagging_upgrade_timer_sec = 0;
 
+  void (*memtag_stack_dlopen_callback)() = nullptr;
   pthread_mutex_t crash_detail_page_lock = PTHREAD_MUTEX_INITIALIZER;
   crash_detail_page_t* crash_detail_page = nullptr;
 };
diff --git a/linker/linker.cpp b/linker/linker.cpp
index a12388c..b0caedd 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -1695,13 +1695,31 @@
   }
 
   // Step 3: pre-link all DT_NEEDED libraries in breadth first order.
+  bool any_memtag_stack = false;
   for (auto&& task : load_tasks) {
     soinfo* si = task->get_soinfo();
     if (!si->is_linked() && !si->prelink_image()) {
       return false;
     }
+    // si->memtag_stack() needs to be called after si->prelink_image() which populates
+    // the dynamic section.
+    if (si->has_min_version(7) && si->memtag_stack()) {
+      any_memtag_stack = true;
+      LD_LOG(kLogDlopen,
+             "... load_library requesting stack MTE for: realpath=\"%s\", soname=\"%s\"",
+             si->get_realpath(), si->get_soname());
+    }
     register_soinfo_tls(si);
   }
+  if (any_memtag_stack) {
+    if (auto* cb = __libc_shared_globals()->memtag_stack_dlopen_callback) {
+      cb();
+    } else {
+      // find_library is used by the initial linking step, so we communicate that we
+      // want memtag_stack enabled to __libc_init_mte.
+      __libc_shared_globals()->initial_memtag_stack = true;
+    }
+  }
 
   // Step 4: Construct the global group. DF_1_GLOBAL bit is force set for LD_PRELOADed libs because
   // they must be added to the global group. Note: The DF_1_GLOBAL bit for a library is normally set
diff --git a/linker/linker_main.cpp b/linker/linker_main.cpp
index 5f5eba4..d6592af 100644
--- a/linker/linker_main.cpp
+++ b/linker/linker_main.cpp
@@ -404,9 +404,6 @@
                      strerror(errno));
     }
   }
-
-  __libc_init_mte(somain->memtag_dynamic_entries(), somain->phdr, somain->phnum, somain->load_bias,
-                  args.argv);
 #endif
 
   // Register the main executable and the linker upfront to have
@@ -496,6 +493,12 @@
     }
     si->increment_ref_count();
   }
+#if defined(__aarch64__)
+  // This has to happen after the find_libraries, which will have collected any possible
+  // libraries that request memtag_stack in the dynamic section.
+  __libc_init_mte(somain->memtag_dynamic_entries(), somain->phdr, somain->phnum, somain->load_bias,
+                  args.argv);
+#endif
 
   linker_finalize_static_tls();
   __libc_init_main_thread_final();
diff --git a/tests/Android.bp b/tests/Android.bp
index a62abab..78c2c10 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -1108,6 +1108,36 @@
 }
 
 cc_test {
+    name: "memtag_stack_dlopen_test",
+    enabled: false,
+    // This does not use bionic_tests_defaults because it is not supported on
+    // host.
+    arch: {
+        arm64: {
+            enabled: true,
+        },
+    },
+    sanitize: {
+        memtag_heap: true,
+        memtag_stack: false,
+    },
+    srcs: [
+        "memtag_stack_dlopen_test.cpp",
+    ],
+    shared_libs: [
+        "libbase",
+    ],
+    data_libs: ["libtest_simple_memtag_stack", "libtest_depends_on_simple_memtag_stack"],
+    data_bins: [
+        "testbinary_depends_on_simple_memtag_stack",
+        "testbinary_depends_on_depends_on_simple_memtag_stack",
+        "testbinary_is_stack_mte_after_dlopen"
+    ],
+    header_libs: ["bionic_libc_platform_headers"],
+    test_suites: ["device-tests"],
+}
+
+cc_test {
     name: "bionic-stress-tests",
     defaults: [
         "bionic_tests_defaults",
diff --git a/tests/NOTICE b/tests/NOTICE
index cc99d20..de95698 100644
--- a/tests/NOTICE
+++ b/tests/NOTICE
@@ -454,3 +454,31 @@
 
 -------------------------------------------------------------------
 
+Copyright (C) 2024 The Android Open Source Project
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+ * Redistributions of source code must retain the above copyright
+   notice, this list of conditions and the following disclaimer.
+ * Redistributions in binary form must reproduce the above copyright
+   notice, this list of conditions and the following disclaimer in
+   the documentation and/or other materials provided with the
+   distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGE.
+
+-------------------------------------------------------------------
+
diff --git a/tests/grp_pwd_test.cpp b/tests/grp_pwd_test.cpp
index 16b8d5a..ddc0fc1 100644
--- a/tests/grp_pwd_test.cpp
+++ b/tests/grp_pwd_test.cpp
@@ -444,16 +444,33 @@
     return result;
   };
 
-  // AID_PRNG_SEEDER (1092) was added in TM-QPR2, but CTS is shared
-  // across Android 13 versions so we may or may not find it in this
-  // test (b/253185870).
-  if (android::base::GetIntProperty("ro.build.version.sdk", 0) == __ANDROID_API_T__) {
-#ifndef AID_PRNG_SEEDER
-#define AID_PRNG_SEEDER 1092
+  // AID_UPROBESTATS (1093) was added in V, but "trunk stable" means
+  // that the 2024Q builds don't have branches like the QPR builds used
+  // to, and are tested with the _previous_ release's CTS.
+  if (android::base::GetIntProperty("ro.build.version.sdk", 0) == __ANDROID_API_U__) {
+#if !defined(AID_UPROBESTATS)
+#define AID_UPROBESTATS 1093
 #endif
-    ids.erase(AID_PRNG_SEEDER);
-    expected_ids.erase(AID_PRNG_SEEDER);
+    ids.erase(AID_UPROBESTATS);
+    expected_ids.erase(AID_UPROBESTATS);
+    if (getpwuid(AID_UPROBESTATS)) {
+      EXPECT_STREQ(getpwuid(AID_UPROBESTATS)->pw_name, "uprobestats");
+    }
   }
+  // AID_VIRTUALMACHINE (3013) was added in V, but "trunk stable" means
+  // that the 2024Q builds don't have branches like the QPR builds used
+  // to, and are tested with the _previous_ release's CTS.
+  if (android::base::GetIntProperty("ro.build.version.sdk", 0) == __ANDROID_API_U__) {
+#if !defined(AID_VIRTUALMACHINE)
+#define AID_VIRTUALMACHINE 3013
+#endif
+    ids.erase(AID_VIRTUALMACHINE);
+    expected_ids.erase(AID_VIRTUALMACHINE);
+    if (getpwuid(AID_VIRTUALMACHINE)) {
+      EXPECT_STREQ(getpwuid(AID_VIRTUALMACHINE)->pw_name, "virtualmachine");
+    }
+  }
+
   EXPECT_EQ(expected_ids, ids) << return_differences();
 }
 #endif
diff --git a/tests/libs/Android.bp b/tests/libs/Android.bp
index 039d1e1..06ee132 100644
--- a/tests/libs/Android.bp
+++ b/tests/libs/Android.bp
@@ -234,6 +234,61 @@
 }
 
 // -----------------------------------------------------------------------------
+// Libraries and binaries used by memtag_stack_dlopen_test tests
+// -----------------------------------------------------------------------------
+cc_test_library {
+    name: "libtest_simple_memtag_stack",
+    sanitize: {
+        memtag_stack: true,
+    },
+    srcs: ["dlopen_testlib_simple.cpp"],
+}
+
+cc_test_library {
+    name: "libtest_depends_on_simple_memtag_stack",
+    sanitize: {
+        memtag_stack: false,
+    },
+    shared_libs: [
+        "libtest_simple_memtag_stack",
+    ],
+    srcs: ["dlopen_testlib_depends_on_simple.cpp"],
+}
+
+cc_binary {
+    name: "testbinary_is_stack_mte_after_dlopen",
+    sanitize: {
+        memtag_stack: false,
+        memtag_heap: true,
+    },
+    srcs: ["testbinary_is_stack_mte_after_dlopen.cpp"],
+}
+
+cc_binary {
+    name: "testbinary_depends_on_simple_memtag_stack",
+    sanitize: {
+        memtag_stack: false,
+        memtag_heap: true,
+    },
+    shared_libs: [
+        "libtest_simple_memtag_stack",
+    ],
+    srcs: ["testbinary_is_stack_mte.cpp"],
+}
+
+cc_binary {
+    name: "testbinary_depends_on_depends_on_simple_memtag_stack",
+    sanitize: {
+        memtag_stack: false,
+        memtag_heap: true,
+    },
+    shared_libs: [
+        "libtest_depends_on_simple_memtag_stack",
+    ],
+    srcs: ["testbinary_is_stack_mte.cpp"],
+}
+
+// -----------------------------------------------------------------------------
 // Libraries used by hwasan_test
 // -----------------------------------------------------------------------------
 cc_test_library {
diff --git a/tests/libs/libs_utils.h b/tests/libs/CHECK.h
similarity index 71%
rename from tests/libs/libs_utils.h
rename to tests/libs/CHECK.h
index 7dae241..2575d5b 100644
--- a/tests/libs/libs_utils.h
+++ b/tests/libs/CHECK.h
@@ -14,14 +14,13 @@
  * limitations under the License.
  */
 
-#ifndef LIBS_UTILS_H
-#define LIBS_UTILS_H
+#pragma once
+
+// Tests proper can use libbase, but libraries for testing dlopen()
+// should probably avoid dependencies other than ones we're specifically
+// trying to test.
 
 #include <assert.h>
-#include <stdio.h>
-#include <stdlib.h>
 
 #define CHECK(e) \
-    ((e) ? static_cast<void>(0) : __assert2(__FILE__, __LINE__, __PRETTY_FUNCTION__, #e))
-
-#endif  // LIBS_UTILS_H
+  ((e) ? static_cast<void>(0) : __assert2(__FILE__, __LINE__, __PRETTY_FUNCTION__, #e))
diff --git a/tests/libs/cfi_test_helper.cpp b/tests/libs/cfi_test_helper.cpp
index c1a7b6d..71cdc89 100644
--- a/tests/libs/cfi_test_helper.cpp
+++ b/tests/libs/cfi_test_helper.cpp
@@ -14,11 +14,10 @@
  * limitations under the License.
  */
 
-#include <assert.h>
 #include <stdint.h>
 #include <stdlib.h>
 
-#include "libs_utils.h"
+#include "CHECK.h"
 
 // This library is built for all targets, including host tests, so __cfi_slowpath may not be
 // present. But it is only used in the bionic loader tests.
diff --git a/tests/libs/cfi_test_helper2.cpp b/tests/libs/cfi_test_helper2.cpp
index 11a6036..d7cd495 100644
--- a/tests/libs/cfi_test_helper2.cpp
+++ b/tests/libs/cfi_test_helper2.cpp
@@ -14,10 +14,9 @@
  * limitations under the License.
  */
 
-#include <assert.h>
 #include <dlfcn.h>
 
-#include "libs_utils.h"
+#include "CHECK.h"
 
 int main(void) {
   void* handle;
diff --git a/libc/platform/bionic/set_abort_message_internal.h b/tests/libs/dlopen_testlib_depends_on_simple.cpp
similarity index 76%
copy from libc/platform/bionic/set_abort_message_internal.h
copy to tests/libs/dlopen_testlib_depends_on_simple.cpp
index 4dff3ac..3652be8 100644
--- a/libc/platform/bionic/set_abort_message_internal.h
+++ b/tests/libs/dlopen_testlib_depends_on_simple.cpp
@@ -26,24 +26,11 @@
  * SUCH DAMAGE.
  */
 
-#pragma once
+#include <stdint.h>
+#include <stdlib.h>
 
-#include <android/set_abort_message.h>
-#include <stddef.h>
-#include <sys/cdefs.h>
+extern "C" bool dlopen_testlib_simple_func();
 
-struct crash_detail_t {
-  const char* name;
-  size_t name_size;
-  const char* data;
-  size_t data_size;
-  crash_detail_t* prev_free;
-};
-
-constexpr auto kNumCrashDetails = 128;
-
-struct crash_detail_page_t {
-  struct crash_detail_page_t* prev;
-  size_t used;
-  struct crash_detail_t crash_details[kNumCrashDetails];
-};
+extern "C" bool dlopen_testlib_call_simple_func() {
+  return dlopen_testlib_simple_func();
+}
diff --git a/tests/libs/preinit_getauxval_test_helper.cpp b/tests/libs/preinit_getauxval_test_helper.cpp
index 2a79b97..53d4cc9 100644
--- a/tests/libs/preinit_getauxval_test_helper.cpp
+++ b/tests/libs/preinit_getauxval_test_helper.cpp
@@ -19,7 +19,7 @@
 #include <unistd.h>
 #include <sys/auxv.h>
 
-#include "libs_utils.h"
+#include "CHECK.h"
 
 static unsigned long g_AT_RANDOM;
 static unsigned long g_AT_PAGESZ;
diff --git a/tests/libs/preinit_syscall_test_helper.cpp b/tests/libs/preinit_syscall_test_helper.cpp
index 9b6b6df..3ca8131 100644
--- a/tests/libs/preinit_syscall_test_helper.cpp
+++ b/tests/libs/preinit_syscall_test_helper.cpp
@@ -19,7 +19,7 @@
 #include <unistd.h>
 #include <sys/auxv.h>
 
-#include "libs_utils.h"
+#include "CHECK.h"
 
 static ssize_t g_result;
 static int g_errno;
diff --git a/tests/libs/stack_tagging_helper.cpp b/tests/libs/stack_tagging_helper.cpp
index 7396dd0..e7e26af 100644
--- a/tests/libs/stack_tagging_helper.cpp
+++ b/tests/libs/stack_tagging_helper.cpp
@@ -28,7 +28,7 @@
 
 #include <bionic/malloc.h>
 
-#include "libs_utils.h"
+#include "CHECK.h"
 
 #if defined(__aarch64__)
 
diff --git a/libc/platform/bionic/set_abort_message_internal.h b/tests/libs/testbinary_is_stack_mte.cpp
similarity index 76%
copy from libc/platform/bionic/set_abort_message_internal.h
copy to tests/libs/testbinary_is_stack_mte.cpp
index 4dff3ac..d8074d5 100644
--- a/libc/platform/bionic/set_abort_message_internal.h
+++ b/tests/libs/testbinary_is_stack_mte.cpp
@@ -26,24 +26,25 @@
  * SUCH DAMAGE.
  */
 
-#pragma once
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
 
-#include <android/set_abort_message.h>
-#include <stddef.h>
-#include <sys/cdefs.h>
+#include "../mte_utils.h"
+#include "CHECK.h"
 
-struct crash_detail_t {
-  const char* name;
-  size_t name_size;
-  const char* data;
-  size_t data_size;
-  crash_detail_t* prev_free;
-};
+#if defined(__BIONIC__) && defined(__aarch64__)
 
-constexpr auto kNumCrashDetails = 128;
+extern "C" int main(int, char**) {
+  int ret = is_stack_mte_on() ? 0 : 1;
+  printf("RAN\n");
+  return ret;
+}
 
-struct crash_detail_page_t {
-  struct crash_detail_page_t* prev;
-  size_t used;
-  struct crash_detail_t crash_details[kNumCrashDetails];
-};
+#else
+
+extern "C" int main(int, char**) {
+  printf("RAN\n");
+  return 1;
+}
+#endif
diff --git a/tests/libs/testbinary_is_stack_mte_after_dlopen.cpp b/tests/libs/testbinary_is_stack_mte_after_dlopen.cpp
new file mode 100644
index 0000000..937ac4c
--- /dev/null
+++ b/tests/libs/testbinary_is_stack_mte_after_dlopen.cpp
@@ -0,0 +1,145 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <condition_variable>
+#include <thread>
+
+#include <dlfcn.h>
+#include <inttypes.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "../mte_utils.h"
+#include "CHECK.h"
+
+#if defined(__BIONIC__) && defined(__aarch64__)
+
+enum State { kInit, kThreadStarted, kStackRemapped };
+
+// We can't use pthread_getattr_np because that uses the rlimit rather than the actual mapping
+// bounds.
+static void find_main_stack_limits(uintptr_t* low, uintptr_t* high) {
+  uintptr_t startstack = reinterpret_cast<uintptr_t>(__builtin_frame_address(0));
+
+  // Hunt for the region that contains that address.
+  FILE* fp = fopen("/proc/self/maps", "re");
+  if (fp == nullptr) {
+    abort();
+  }
+  char line[BUFSIZ];
+  while (fgets(line, sizeof(line), fp) != nullptr) {
+    uintptr_t lo, hi;
+    if (sscanf(line, "%" SCNxPTR "-%" SCNxPTR, &lo, &hi) == 2) {
+      if (lo <= startstack && startstack <= hi) {
+        *low = lo;
+        *high = hi;
+        fclose(fp);
+        return;
+      }
+    }
+  }
+  abort();
+}
+
+template <typename Fn>
+unsigned int fault_new_stack_page(uintptr_t low, Fn f) {
+  uintptr_t new_low;
+  uintptr_t new_high;
+  volatile char buf[4096];
+  buf[4095] = 1;
+  find_main_stack_limits(&new_low, &new_high);
+  if (new_low < low) {
+    f();
+    return new_high;
+  }
+  // Useless, but should defeat TCO.
+  return new_low + fault_new_stack_page(low, f);
+}
+extern "C" int main(int argc, char** argv) {
+  if (argc < 2) {
+    return 1;
+  }
+  const char* path = argv[1];
+  CHECK(access(path, F_OK) == 0);  // Verify test setup.
+  CHECK(!is_stack_mte_on());
+  std::mutex m;
+  std::condition_variable cv;
+  State state = kInit;
+
+  bool is_early_thread_mte_on = false;
+  std::thread early_th([&] {
+    {
+      std::lock_guard lk(m);
+      state = kThreadStarted;
+    }
+    cv.notify_one();
+    {
+      std::unique_lock lk(m);
+      cv.wait(lk, [&] { return state == kStackRemapped; });
+    }
+    is_early_thread_mte_on = is_stack_mte_on();
+  });
+  {
+    std::unique_lock lk(m);
+    cv.wait(lk, [&] { return state == kThreadStarted; });
+  }
+  void* handle = dlopen(path, RTLD_NOW);
+  {
+    std::lock_guard lk(m);
+    state = kStackRemapped;
+  }
+  cv.notify_one();
+  CHECK(handle != nullptr);
+  CHECK(is_stack_mte_on());
+
+  bool new_stack_page_mte_on = false;
+  uintptr_t low;
+  uintptr_t high;
+  find_main_stack_limits(&low, &high);
+  fault_new_stack_page(low, [&] { new_stack_page_mte_on = is_stack_mte_on(); });
+  CHECK(new_stack_page_mte_on);
+
+  bool is_late_thread_mte_on = false;
+  std::thread late_th([&] { is_late_thread_mte_on = is_stack_mte_on(); });
+  late_th.join();
+  early_th.join();
+  CHECK(is_late_thread_mte_on);
+  CHECK(is_early_thread_mte_on);
+  printf("RAN\n");
+  return 0;
+}
+
+#else
+extern "C" int main(int, char**) {
+  return 1;
+}
+#endif
diff --git a/tests/memtag_stack_dlopen_test.cpp b/tests/memtag_stack_dlopen_test.cpp
new file mode 100644
index 0000000..68ddb81
--- /dev/null
+++ b/tests/memtag_stack_dlopen_test.cpp
@@ -0,0 +1,117 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <thread>
+
+#include <dlfcn.h>
+#include <stdlib.h>
+
+#include <gtest/gtest.h>
+
+#include <android-base/silent_death_test.h>
+#include <android-base/test_utils.h>
+#include "mte_utils.h"
+#include "utils.h"
+
+TEST(MemtagStackDlopenTest, DependentBinaryGetsMemtagStack) {
+#if defined(__BIONIC__) && defined(__aarch64__)
+  if (!running_with_mte()) GTEST_SKIP() << "Test requires MTE.";
+  if (is_stack_mte_on())
+    GTEST_SKIP() << "Stack MTE needs to be off for this test. Are you running fullmte?";
+
+  std::string path =
+      android::base::GetExecutableDirectory() + "/testbinary_depends_on_simple_memtag_stack";
+  ExecTestHelper eth;
+  std::string ld_library_path = "LD_LIBRARY_PATH=" + android::base::GetExecutableDirectory();
+  eth.SetArgs({path.c_str(), nullptr});
+  eth.SetEnv({ld_library_path.c_str(), nullptr});
+  eth.Run([&]() { execve(path.c_str(), eth.GetArgs(), eth.GetEnv()); }, 0, "RAN");
+#else
+  GTEST_SKIP() << "requires bionic arm64";
+#endif
+}
+
+TEST(MemtagStackDlopenTest, DependentBinaryGetsMemtagStack2) {
+#if defined(__BIONIC__) && defined(__aarch64__)
+  if (!running_with_mte()) GTEST_SKIP() << "Test requires MTE.";
+  if (is_stack_mte_on())
+    GTEST_SKIP() << "Stack MTE needs to be off for this test. Are you running fullmte?";
+
+  std::string path = android::base::GetExecutableDirectory() +
+                     "/testbinary_depends_on_depends_on_simple_memtag_stack";
+  ExecTestHelper eth;
+  std::string ld_library_path = "LD_LIBRARY_PATH=" + android::base::GetExecutableDirectory();
+  eth.SetArgs({path.c_str(), nullptr});
+  eth.SetEnv({ld_library_path.c_str(), nullptr});
+  eth.Run([&]() { execve(path.c_str(), eth.GetArgs(), eth.GetEnv()); }, 0, "RAN");
+#else
+  GTEST_SKIP() << "requires bionic arm64";
+#endif
+}
+
+TEST(MemtagStackDlopenTest, DlopenRemapsStack) {
+#if defined(__BIONIC__) && defined(__aarch64__)
+  // If this test is failing, look at crash logcat for why the test binary died.
+  if (!running_with_mte()) GTEST_SKIP() << "Test requires MTE.";
+  if (is_stack_mte_on())
+    GTEST_SKIP() << "Stack MTE needs to be off for this test. Are you running fullmte?";
+
+  std::string path =
+      android::base::GetExecutableDirectory() + "/testbinary_is_stack_mte_after_dlopen";
+  std::string lib_path =
+      android::base::GetExecutableDirectory() + "/libtest_simple_memtag_stack.so";
+  ExecTestHelper eth;
+  std::string ld_library_path = "LD_LIBRARY_PATH=" + android::base::GetExecutableDirectory();
+  eth.SetArgs({path.c_str(), lib_path.c_str(), nullptr});
+  eth.SetEnv({ld_library_path.c_str(), nullptr});
+  eth.Run([&]() { execve(path.c_str(), eth.GetArgs(), eth.GetEnv()); }, 0, "RAN");
+#else
+  GTEST_SKIP() << "requires bionic arm64";
+#endif
+}
+
+TEST(MemtagStackDlopenTest, DlopenRemapsStack2) {
+#if defined(__BIONIC__) && defined(__aarch64__)
+  // If this test is failing, look at crash logcat for why the test binary died.
+  if (!running_with_mte()) GTEST_SKIP() << "Test requires MTE.";
+  if (is_stack_mte_on())
+    GTEST_SKIP() << "Stack MTE needs to be off for this test. Are you running fullmte?";
+
+  std::string path =
+      android::base::GetExecutableDirectory() + "/testbinary_is_stack_mte_after_dlopen";
+  std::string lib_path =
+      android::base::GetExecutableDirectory() + "/libtest_depends_on_simple_memtag_stack.so";
+  ExecTestHelper eth;
+  std::string ld_library_path = "LD_LIBRARY_PATH=" + android::base::GetExecutableDirectory();
+  eth.SetArgs({path.c_str(), lib_path.c_str(), nullptr});
+  eth.SetEnv({ld_library_path.c_str(), nullptr});
+  eth.Run([&]() { execve(path.c_str(), eth.GetArgs(), eth.GetEnv()); }, 0, "RAN");
+#else
+  GTEST_SKIP() << "requires bionic arm64";
+#endif
+}
diff --git a/libc/platform/bionic/set_abort_message_internal.h b/tests/mte_utils.h
similarity index 77%
copy from libc/platform/bionic/set_abort_message_internal.h
copy to tests/mte_utils.h
index 4dff3ac..6e8385c 100644
--- a/libc/platform/bionic/set_abort_message_internal.h
+++ b/tests/mte_utils.h
@@ -28,22 +28,16 @@
 
 #pragma once
 
-#include <android/set_abort_message.h>
-#include <stddef.h>
-#include <sys/cdefs.h>
+#if defined(__BIONIC__) && defined(__aarch64__)
 
-struct crash_detail_t {
-  const char* name;
-  size_t name_size;
-  const char* data;
-  size_t data_size;
-  crash_detail_t* prev_free;
-};
+__attribute__((target("mte"))) static bool is_stack_mte_on() {
+  alignas(16) int x = 0;
+  void* p = reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(&x) + (1UL << 57));
+  void* p_cpy = p;
+  __builtin_arm_stg(p);
+  p = __builtin_arm_ldg(p);
+  __builtin_arm_stg(&x);
+  return p == p_cpy;
+}
 
-constexpr auto kNumCrashDetails = 128;
-
-struct crash_detail_page_t {
-  struct crash_detail_page_t* prev;
-  size_t used;
-  struct crash_detail_t crash_details[kNumCrashDetails];
-};
+#endif
diff --git a/tests/unistd_test.cpp b/tests/unistd_test.cpp
index 88f5851..6c08972 100644
--- a/tests/unistd_test.cpp
+++ b/tests/unistd_test.cpp
@@ -753,22 +753,36 @@
 
 TEST(UNISTD_TEST, pathconf_fpathconf) {
   TemporaryFile tf;
-  long rc = 0L;
+  long l;
+
   // As a file system's block size is always power of 2, the configure values
   // for ALLOC and XFER should be power of 2 as well.
-  rc = pathconf(tf.path, _PC_ALLOC_SIZE_MIN);
-  ASSERT_TRUE(rc > 0 && powerof2(rc));
-  rc = pathconf(tf.path, _PC_REC_MIN_XFER_SIZE);
-  ASSERT_TRUE(rc > 0 && powerof2(rc));
-  rc = pathconf(tf.path, _PC_REC_XFER_ALIGN);
-  ASSERT_TRUE(rc > 0 && powerof2(rc));
+  l = pathconf(tf.path, _PC_ALLOC_SIZE_MIN);
+  ASSERT_TRUE(l > 0 && powerof2(l));
+  l = pathconf(tf.path, _PC_REC_MIN_XFER_SIZE);
+  ASSERT_TRUE(l > 0 && powerof2(l));
+  l = pathconf(tf.path, _PC_REC_XFER_ALIGN);
+  ASSERT_TRUE(l > 0 && powerof2(l));
 
-  rc = fpathconf(tf.fd, _PC_ALLOC_SIZE_MIN);
-  ASSERT_TRUE(rc > 0 && powerof2(rc));
-  rc = fpathconf(tf.fd, _PC_REC_MIN_XFER_SIZE);
-  ASSERT_TRUE(rc > 0 && powerof2(rc));
-  rc = fpathconf(tf.fd, _PC_REC_XFER_ALIGN);
-  ASSERT_TRUE(rc > 0 && powerof2(rc));
+  l = fpathconf(tf.fd, _PC_ALLOC_SIZE_MIN);
+  ASSERT_TRUE(l > 0 && powerof2(l));
+  l = fpathconf(tf.fd, _PC_REC_MIN_XFER_SIZE);
+  ASSERT_TRUE(l > 0 && powerof2(l));
+  l = fpathconf(tf.fd, _PC_REC_XFER_ALIGN);
+  ASSERT_TRUE(l > 0 && powerof2(l));
+
+  // Check that the "I can't answer that, you'll have to try it and see"
+  // cases don't set errno.
+  int names[] = {
+      _PC_ASYNC_IO, _PC_PRIO_IO, _PC_REC_INCR_XFER_SIZE, _PC_REC_MAX_XFER_SIZE, _PC_SYMLINK_MAX,
+      _PC_SYNC_IO,  -1};
+  for (size_t i = 0; names[i] != -1; i++) {
+    errno = 0;
+    ASSERT_EQ(-1, pathconf(tf.path, names[i])) << names[i];
+    ASSERT_ERRNO(0) << names[i];
+    ASSERT_EQ(-1, fpathconf(tf.fd, names[i])) << names[i];
+    ASSERT_ERRNO(0) << names[i];
+  }
 }
 
 TEST(UNISTD_TEST, _POSIX_constants) {
diff --git a/tools/update_notice.sh b/tools/update_notice.sh
index c45311a..69e090c 100755
--- a/tools/update_notice.sh
+++ b/tools/update_notice.sh
@@ -11,4 +11,4 @@
 python3 ./libc/tools/generate_notice.py linker > linker/NOTICE
 python3 ./libc/tools/generate_notice.py tests > tests/NOTICE
 python3 ./libc/tools/generate_notice.py tools > tools/NOTICE
-git diff --exit-code HEAD libc/NOTICE
+git diff --exit-code HEAD */NOTICE